Over juicing 400 watt bulb with dimmable ballast.

First of all, I know you're not supposed to run a bulb on any wattage other than that which it is rated for; and you are especially not supposed to run a bulb at higher than it is rated for, obviously. I have wondered what might actually happen if one were to ignite a 400 watt bulb at 600 watts, for example, and sort of imagined that the bulb might fail catastrophically.

That said a lot of the newer digital ballasts are dimmable, but I still prefer to run the appropriate bulb at the appropriate wattage and put a 400 watt MH Conversion bulb into a dimmable 600 watt Lumatek ballast to run at 400 watts for vegging plants.

So basically what just happened today is I am cleaning the room, vacuuming a bit and thru a series of events the knob on the Lumatek ballast catches on a piece of paneling as it knocked over or something and it turns up to 600 watts! I immediately went to check it, put it back down to 400. Then a minute or so later decided I better just unplug it so that I can examine the bulb. The bulb did seem to get brighter until I turned it down, but it doesn't appear to be damaged. It was only on the 600 watt setting for maybe 40 seconds, and I am thinking it likely didn't even have a chance to warm up to that setting completely.

This ever happen to anybody else?

Nope, never did this.
You got the right idea - match the ballast setting to the bulb.
You probably just took some life out of your bulb, prematurely aging the filament.

You may know some (lumatek) ballast have a boost setting, to allow you to get more out of bulb than the manufacturer's ratings. I think Lumatek calls this 'super lumens' and has an SL setting on the ballast. I think it boost output by 10%. You can use the same bulb & give it more wattage for more light when needed (e.g., flowering). I got this setting, but have not used it. I also don't run a lamp at a lower setting.

A guy came into my thread and said he Always runs his 400w bulbs at the 600w setting. No implosions just cuts the life down...

I would still consider him lucky, wouldn't want to be doing that with a cheap bulb. Even though it is rare, the arc tube can potentially explode if the lamp fails violently.

Also imagine you aren't getting the full efficiency\light output that a 600 watt lamp would provide.